Added a console warning when <picture><source src></picture> is used.

Source/core/html/HTMLImageElement.cpp

Index: Source/core/html/HTMLImageElement.cpp
diff --git a/Source/core/html/HTMLImageElement.cpp b/Source/core/html/HTMLImageElement.cpp
index e738685e6f1267e4894d29acbb622019399bce0d..395e76bac8616bec0be38c7d3b4613b5cacef96c 100644
--- a/Source/core/html/HTMLImageElement.cpp
+++ b/Source/core/html/HTMLImageElement.cpp
@@ -41,6 +41,7 @@
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/parser/HTMLParserIdioms.h"
 #include "core/html/parser/HTMLSrcsetParser.h"
+#include "core/inspector/ConsoleMessage.h"
 #include "core/rendering/RenderImage.h"
 #include "platform/MIMETypeRegistry.h"
 #include "platform/RuntimeEnabledFeatures.h"
@@ -282,6 +283,10 @@ ImageCandidate HTMLImageElement::findBestFitImageFromPictureParent()
             continue;
 
         HTMLSourceElement* source = toHTMLSourceElement(child);
+        if (!source->fastGetAttribute(srcAttr).isNull()) {
+            document().addConsoleMessage(ConsoleMessage::create(RenderingMessageSource, WarningMessageLevel, "<source src> with a <picture> parent is invalid and therefore ignored. Use <source srcset> instead."));

[Mike West, 2014/08/13 14:29:30]

You can drop this message here, and add it to the deprecation message list in
UseCounter.cpp:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+            UseCounter::countDeprecation(document(), UseCounter::PictureSourceSrc);
+        }
         String srcset = source->fastGetAttribute(srcsetAttr);
         if (srcset.isEmpty())
             continue;